In a political career already noted for historic breakthroughs, President Obama is poised in 2012 to chalk up another: the nation’s first $1 billion candidate.

With the 2012 election more than 19 months out, Mr. Obama’s team is preparing to again tap into the army of small-dollar donors who powered his record-breaking 2008 money haul. Replicating that success will depend in part on whether the president can convince his most fervent supporters to overlook disappointments on campaign promises such as immigration reform and closing the prison at U.S. Naval Base Guantanamo Bay, Cuba.

As the incumbent this time, Mr. Obama has advantages that could catapult him beyond that 2008 total of $745 million - including the bully pulpit of the presidency itself and access to institutional money that wasn’t there when he ran as an outsider.

Add to that the 13 million grass-roots supporters from the 2008 campaign — a list that has been dutifully maintained by the Democratic National Committee under the moniker of Organizing for America — and 2012 looks like an eye-popping year for political fundraising.

“Just given the base he begins with and the ability to go out and raise money online now, I expect he will end up being the first billion-dollar candidate,” said Anthony J. Corrado Jr., a government professor at Colby College.

At the same time, Mr. Corrado noted, the task won’t be “as easy as people suggest” given that presidents running for re-election historically experience drop-offs among previous donors.

Small-dollar army

In 2008, 34 percent of the cash Mr. Obama raised after securing the Democratic nomination came from donations of $200 or less, according to the nonpartisan Campaign Finance Institute. That proportion compensated for the campaign’s ban on money from lobbyists and political action committees and was a source of pride for Mr. Obama, a former community organizer who used the donations to bolster his grass-roots credentials.

It’s an open question how many of the small-dollar donors will return, but CFI Executive Director Michael Malbin said the president is likely to get much more support from major donors who were locked up early in 2008 by candidate Hillary Rodham Clinton.

Democratic sources say Mr. Obama is likely to file paperwork for his re-election campaign late this month or in early April — but that doesn’t mean he’ll be hitting the campaign trail any time soon.

Instead, filing the papers will give campaign manager Jim Messina, his former White House deputy chief of staff, a chance to set up shop in Chicago with deputies Jennifer O’Malley Dillon, the DNC executive director, and Julianna Smoot, a veteran Democratic fundraiser and former White House social secretary.

Wild card

One fundraising factor beyond the president’s control is the Republican presidential nominee.

The GOP could pick a “mainstream candidate or they could pick a goofball,” said University of Virginia political science professor Larry Sabato, adding that it’s a lot more likely that Mr. Obama will surpass $1 billion if the GOP nominee “scares” Democrats.

Against the front-runners in the crowded field of GOP contenders, Mr. Obama is polling moderately well.

He runs more than 5 percentage points ahead of former Arkansas Gov. Mike Huckabee and former Massachusetts Gov. Mitt Romney, according to Real Clear Politics, and runs ahead of former House Speaker Newt Gingrich and former Minnesota Gov. Tim Pawlenty by 14 and 15 points, respectively.

Still, the surge in Internet contributions to tea-party-backed candidates during the 2010 congressional elections is evidence that the GOP may be able to mimic Mr. Obama’s success with small donors by tapping into a new base of conservative contributors.

The 2010 elections also indicate that the GOP nominee will have significant outside help next year. American Crossroads, an advocacy group founded by former Bush strategist Karl Rove, earlier this month announced a goal of raising $120 million to spend against Mr. Obama and other Democrats in 2012.

Yet after being trounced in November, Democrats aren’t likely to be caught flatfooted again.

They are gearing up their own counterweights to Mr. Rove’s group, including American Bridge, led by former Maryland Lt. Gov. Kathleen Kennedy Townsend and David Brock, the founder of Media Matters.

Rebuilding the base

The Democrats want to expand the electoral map, but analysts say the president will have a tough time hanging on to Virginia, Indiana and North Carolina — all previously red states that Mr. Obama picked up last time. The big focus will again be on presidential bellwethers such as Ohio and Florida, where disappointment among Hispanic voters could be an issue.

Some core Democratic voting blocs, such as immigrant rights groups, say the president may not be able to count on their enthusiasm in 2012.

“He’s had about two years to take positive steps on immigration issues, and if you kind of do the tally of where we are right now it’s overwhelmingly a profound disappointment,” said Chung-Wha Hong, executive director of the New York Immigration Coalition, which has called on Mr. Obama to sign an executive order halting deportations. “I think there’s still a lot of good will, that people are willing to give him a chance, but I think that window is really closing.”

The failure to close the prison at Guantanamo Bay, coupled with the detainment of accused WikiLeaks figure Pfc. Bradley Manning, has other Obama backers wavering.

“The lesson is clear, and soldiers take note: You’re better off committing a war crime than exposing one,” Code Pink co-founder Medea Benjamin recently wrote on the Huffington Post about Pfc. Manning, who is suspected of leaking tens of thousands of government documents to the website WikiLeaks.

On the other hand, Mr. Obama has delivered on promises to gay-rights advocates, pushing Congress last year to lift the ban on gays serving openly in the military and announcing this year that his administration no longer would defend the Defense of Marriage Act, which defined marriage at the federal level as the union of a man and a woman.

Above the fray

Mr. Obama may still have some work to do in rebuilding the 2008 coalition, but don’t look for active campaigning anytime soon.

“You don’t want to be running for re-election” too early, Mr. Sabato said. “You don’t want to be a mere candidate again because you do lose some of the magic of the presidency.”

As of now, one of the best things Mr. Obama has going for him is the uncertainty surrounding the Republican field.

Mr. Corrado suggested that Mr. Obama may take a page from the 2004 campaign playbook of President George W. Bush: Get out front by deploying cash to define the eventual nominee, as Mr. Bush’s campaign did with Sen. John F. Kerry, spending tens of millions of dollars in advertising after the Massachusetts Democrat emerged as his party’s pick.

“I think we’ll see a similar dynamic in 2012,” he said. “The advantage that the Republican nominee will have this time is they’ll be capable of raising much more money than candidates in the past.”